stop the unit and listen for deceleration noises. Noises
and drain solenoid valve. This would probably show up
indicate that bearings, seals, or rotating components
in leaking fuel from the plenum drain during
may be failing, causing excessive drag on the unit.
deceleration when the engine is stopped. To check the
solenoid, remove the electrical connector from the oil
Smooth deceleration indicates no excessive drag
pressure switch, remove the fuel line from the fuel
on the unit. Therefore, the turbine is not converting the
atomizer, and place the end of the line in a bucket.
energy it receives properly or its airflow is obstructed.
Motor the unit and if the solenoid valve is OK, no fuel
Check the air intake and exhaust ducting. After the unit
should flow through the line.
cools, check the turbine wheel and flame tube for
damage and excessive carbon.
Premature opening of the fuel shutoff and drain
If the temperature is low and the unit fails to
c h a m b e r b e f o r e t h e r e i s s u ffi c i e n t a i r f l ow f o r
accelerate, the fuel and control air pressure should be
combustion. This causes the fuel to puddle. Then,
observed. The engine can accelerate only if the control
w h e n l i g h t o ff ( c o m bu s t i o n ) fi n a l l y o c c u r s , a
air pressure acts on the fuel scheduling valve's
noticeable flame shoots out the exhaust until the excess
diaphragm, and calls for increasing fuel flow to keep
fuel burns off. This fault can be caused by a faulty
pace with increasing airflow. If the control air pressure
oil-pressure switch. To check the switch, listen for the
system develops any appreciable leakage, fuel
sound of the igniter plug when the start switch is
pressure will be too low to allow the unit to reach full
actuated. Remember, the ignition unit and fuel shutoff
speed. If the air pressure is low or fails to rise with
and drain solenoid valve are sequentially activated at
engine speed, check for leaks at the inlet air orifice on
2.5 to 3.5 psig (about 10-percent engine rpm). If the
the compressor housing, the control air filter, all of the
igniter can be heard as soon as the start switch is
control air plumbing, and acceleration and
actuated, the oil-pressure switch is bad.
overtemperature thermostat. You should also check the
d i a p h r a g m s o f t h e f u e l s c h e d u l i n g va l ve , t h e
If fuel and ignition appear to be sequenced
mechanical governor, and the air-pressure-ratio
properly by the oil-pressure switch, stop the unit and
disconnect the fuel line from the fuel atomizer.
Connect a pressure gauge to the line, motor the unit,
To check the mechanical governor diaphragm and
and read the "cracking" pressure. If the pressure is
the air-pressure-ratio solenoid valve, observe the
higher than specification, the high pressure is causing
high-speed adjustment screw on the fuel control while
too much fuel flow through the fuel atomizer by
disconnecting the air-pressure-ratio solenoid valve.
prematurely opening its flow divider valve. If
The adjustment screw should extend outward from the
"cracking" pressure is normal, the fuel atomizer is
housing when the plug is disconnected and retract into
probably faulty. During the check and repair of the fuel
the fuel control when the electrical plug is
atomizer, check the combustion liner for deformation,
reconnected. If the adjustment screw retracts, the
excessive carbon, or cracks that may affect the unit's
diaphragm and valve are working.
If no leaks are discovered and the air-
pressure-ratio solenoid valve and diaphragm are
Engine Lights Off But Will Not Accelerate
operating, the acceleration and overtemperature
thermostat could be bleeding off too soon (set too low).
The cause of an engine not accelerating may be too
The thermostat can be checked by using the air control
little turbine power being developed to meet the
valve and air gauge assembly feature incorporated in
engine's requirements. The power requirements are
the gas turbine engine analyzer (described later in this
reflected by the turbine discharge temperature (TDT).
text). Disconnect the control air line from the fuel
Therefore, if the motoring engine "hangs" during
control to the thermostat and install the analyzer's air
control assembly feature in-line. Run the turbine unit
with the air control valve closed and observe the unit's
overtemperature thermostat), the engine is requiring
TDT and the analyzer's air gauge. If the analyzer gauge
more than a normal amount of power from the turbine.
indicates a low air pressure, the unit has a control air
Feel around the turbine plenum, tail pipe, and
leak; if the unit accelerates to governed speed, the
thermostat is faulty and must be replaced or reset. If the
modulating and shutoff valve to ensure that it is not
unit has no air leaks, the thermostats check good, and it
has sufficient fuel pressure but still does not accelerate
stuck open. If no problems are found in these areas,